.TH std::ctype::is,std::ctype::do_is 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::ctype::is,std::ctype::do_is \- std::ctype::is,std::ctype::do_is

.SH Synopsis
   Defined in header <locale>
   public:                                                                         \fB(1)\fP
   bool is( mask m, CharT c ) const;
   public:                                                                         \fB(2)\fP
   const CharT* is( const CharT* low, const CharT* high, mask* vec ) const;
   protected:                                                                      \fB(3)\fP
   virtual bool do_is( mask m, CharT c ) const;
   protected:
   virtual const CharT* do_is( const CharT* low, const CharT* high, mask* vec )    \fB(4)\fP
   const;

   1,2) Public member function, calls the protected virtual member function do_is of
   the most derived class.
   3) Checks if the character c is classified by the mask m.
   4) For every character in the character array [low, high), identifies the complete
   classification mask (e.g. digit|xdigit|alnum|print|graph for the digit '0' in the
   default locale), and stores the masks in the corresponding elements of the array
   pointed to by vec.

.SH Parameters

   c    - character to classify
   m    - mask to use for classifying a single character
   low  - pointer to the first character in an array of characters to classify
   high - one past the end pointer for the array of characters to classify
   vec  - pointer to the first element of the array of masks to fill

.SH Return value

   1,3) true if c is classified by m.
   2,4) high

.SH Example


// Run this code

 #include <cstddef>
 #include <iostream>
 #include <locale>
 #include <utility>
 #include <vector>

 // utility wrapper to make locale-bound facets destructible
 template<class Facet>
 struct deletable_facet : Facet
 {
     template<class ...Args>
     deletable_facet(Args&& ...args) : Facet(std::forward<Args>(args)...) {}
     ~deletable_facet() {}
 };

 int main()
 {
     // classify a single character using the default locale
     auto& f = std::use_facet<std::ctype<char>>(std::locale());
     char c = '0';
     if (f.is(std::ctype_base::digit, c)) // or isdigit(c, locale());
         std::cout << '\\'' << c << "' is a digit\\n";

     // classify every character in a string using a named locale
     deletable_facet<std::ctype_byname<wchar_t>> f2("en_US.utf8");
     std::wstring str = L"z\\u00df\\u6c34\\U0001d10b";
     std::vector<std::ctype_base::mask> vec(str.size());
     f2.is(&str[0], &str[0] + str.size(), &vec[0]);

     for (std::size_t n = 0; n < str.size(); ++n)
     {
         std::cout << std::hex << "U+" << static_cast<wint_t>(str[n]) << " is: ";
         if (vec[n] & std::ctype_base::alnum)
             std::cout << "alnum";
         if (vec[n] & std::ctype_base::punct)
             std::cout << "punct";
         std::cout << '\\n';
     }
 }

.SH Output:

 '0' is a digit
 U+7a is: alnum
 U+df is: alnum
 U+6c34 is: alnum
 U+1d10b is: punct

.SH See also

            classifies a character or a character sequence, using the classification
   is       table
            \fI(public member function of std::ctype<char>)\fP
   iswctype classifies a wide character according to the specified LC_CTYPE category
            \fI(function)\fP
